Nozzle for rocket motors



Jan. 29, 1952 Q N f||C;K|\/|A|\,|4 2,583,570

NOZZLE FOR ROCKET MOTORS Fl'ed June 28, 1945 grvue/WLOP Clara-LEE N Hickman @gawd/MMM @ktm/ump' Patented Jan. 29, 1952 NozzLE FOR ROCKET MOTORS Clarence N. Hickman, Jackson Heights, N. Y., assignorto the United States of America` asv represented by the Secretary of War Application June` 28, 1945, Serial No. 602,141

9 Claims. (Cl. 102-49) (Granted under :the act of `March 3, 1883,as

amended April 30, 1928; 370 0. G.. 75'!) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the paymentl to me of any royalty thereon.

This invention relates to rockets and more particularly to an'adjustable nozzle for rockets.

y A rocket motor consistsv essentially of a cylindrical chamber for containing a propellent composition which upon ignition and burning generates a hot gaseous fluid under pressure. This huid, consisting of the combustion products of the propellent material,A is discharged Aat a high velocity through a'Venturi-like nozzle, located preferably at the rear of the motor chamber.

In Order to obtain a high specic impulse for rapidly accelerated' rockets a propellant having a high burning rate and high heat of explosion is preferred. This type of propellant is characterized by the fact that its burning rate is variable with temperature. This invention is concerned primarily with the problem of providing means compensating for the effect upon rocket performance of this change in burning rate of the propellant with changes in temperature.

' The pressure of the fluid within a rocket motor is'determined by the equilibrium between the rate at which the combustion Vproducts are formed and the rate at `which they are ejected from the venturi. The rate of ejection of these combustion products is roughly proportional to the pressure within'the motor chamber, and the rate at which they are formed depends upon the rate of burning cf the propellant. This rate of burning is proportional to pressure and depends also upon thc temperature of the propellent material.

rlhe inuence of ambient temperature upon the equilibrium pressure within a rocket motor causes the pressure to increase rapidly with ambient temperature.

The detrimental effects caused by temperature variations will be made more apparent by considering some design and operation factors affecting rockets. It is `generally desirable to design a rocket with a minimum dead lload and since it is the weight of the motor chamber that contributes chiey to the dead load, the Walls of the motor chamber are made just thick enough, allowing a reasonable factor of safety, to withstand the internal pressure at which the rocket is to operate. Now the optimum propellent loading which could be safely used at low temperatures would cause the motor chamber to rupture upon burning at high temperatures because of the increase in burning rate of the propellant at this high temperature. Consequently, in order to insure against the possibility of motor` chamber rupture of these high temperatures, the surface of the propellant must be reduced or elsethe throat area of the nozzle must be increased-. This reduction in surface area of` propellant, o r increase in nozzle throat, results also in a reduction in effective velocity and maximum range at the lower temperatures. j I In designing rockets for different temperature ranges, different nozzles may be selected to shift the point of maximum effective discharge velocity of the combustion product relativeto the itemperature scalel so that the maximum may Aoccur at a relatively high, low, or intermediate temperature. In this invention it is proposed to utilize a nozzle having an adjustable throatk so that the maximum effective discharge velocity and maximum range may be acquired at all temperatures Within the operating limits with a single nozzle. Since thepressure rises` steeply with temperature it follows that the burning time of Vpowder grains having a unifor'mweb thickness will decrease as the temperature increases. This eliect of temperature onv` burning time placesfurther restrictions on theA design and performance of rockets,.particularly rapidly accelerated rockets. It has been discovered that the dispersion encountered inrockets increases asthe third power of the burning time. Consequently, if a loading arrangement were to'be" designed to givei'the lowest possible dispersion at low temperature by raising the pressure level in the motor to shorten the burning time, the pressure developed` "at higher temperatures would be excessive, resulting in fracture of the motor chamber. To insure a reasonable maximum pressure over a specified temperature range, the pressure level must be reducd to such a value that the dispersion encountered at the lower temperatures is greatly increased. By virtue of thisV invention however it is possible to design a'rocket which will have a minimum dispersion throughout the operating temperature range, and this dispersion will vremain substantially constant irrespective of the temperature. Another advantage of the structure characterized by this invention is that regular burning of the propellant may be obtained at all operating temperatures. In the present design of rockets the propellant burns irregularly at very low temperatures because its burning rate at these temperatures is too low tocause a sufoient pressure to be built up within the-chamber to sustain burning.-l i Y :The specific nature of the inventionas wellzaS other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawlng 1n which:

Fig. lv is an enlarged elevational view in sect1on of rocket motor having a Venturi-like nozzle with a manually adjustable throat.

Fig. 2 is an elevational view in section of a modification of Fig. 1. y K

Fig. 3 is an elevational view in section of a In Fig. 3 there is shown a hollow housing 2 defining motor chamber 3| having at its rear an inwardly flared entrance portion 32, leading to a hollow cylindrical section 33 having an interior rocket motor having a straight cylindrical nozzle with a manually adjustable throat.

Fig. 4 is an elevational view in section of a modification of Fig. 3.

Fig. 5 is an elevational view in section of a rocket motor having a straight cylindrical nozzle with an automatically adjustable throat.

Fig. 6 is an elevational view in section of a modification of the rocket shown in Fig. 5.

In Fig. 1 of the drawings there is shown a hollow housing I defining a rocket motor combustion chamber IU which has an inwardly flared end, leading to a constricted cylindrical flange portion II. This flange portion II is internally 'threaded as at I2 to accommodate an adjustable nozzle I3. The interior of nozzle I3 is shaped to fform a Venturi-like construction, being provided with front and rear portions I4 and I5, respectively, inwardly and outwardly flared to and from a constricted throat portion I 6.

One end I8 of a burster tube I'I is conical in form and extends into the cylindrical flange portion II. This end of the burster tube I1 is provided with four centralizing spiders I9, which are provided for accurately centering the tube within the throat opening to insure that the annular throat will be perfectly symmetrical. By adjusting the longitudinal position of the nozzle I3, relative to the conical end of the burster tube I1 by means of the threaded engagement therebetween, the effective cross-sectional area of the nozzle throat I6 may be varied to provide for an 'increase or decrease in the ratio of the burning -surface of the propellant to the throat area of the Venturi, sufficient to compensate for temperature variations. Preferably a portion of threads I2 on the nozzle are milled smooth so that the temperature indications may be engraved thereon. In this manner the effective throat area may be easily and certainly adjusted in the field by rotation of nozzle I3.

In Fig. 2 there is disclosed a modification wherein a motor casing 2I and a Venturi nozzle 22 are integrally formed to provide an inwardly flared entrance 25, leading to a throat 24 of the nozzle and a rearwardly flared exit 23 for expanding the discharge gases. In this modification a yburster tube 26 is terminated well forward of the throat 24 and has its outer cylindrical surface threaded to receive a conical shaped adapter 2l. This adapter 21 is provided with centering ns 28 spaced about its periphery and a cylindrical recess 29 which is internally threaded so as to be adjustable on the burster tube 26 to vary the Vcross-sectional area of the annular jet formed by the outer surface of the adapter 2'! and the nozzle throat 24.

Recent tests reveal that a rocket equipped with a cylindrical throat extension has a range and dispersion substantially equivalent to that obtained with a rocket motor having a flared venturi. Thus in accordance with this invention a rocket motor may be provided with a nozzlev of adjustable throat area without the necessity of extending the burster tube to form an annular 39 of reduced diameter. An adjustable cone 34 of streamlined configuration is secured to a support ring 35 by means of four centralizing spiders 36, opposite ends of which are welded to the tapered portion of the cone 34 and the support ring 35, respectively. Cone 34 thus defined an annular discharge passage in cooperation with housing I. The ring 35 is provided with internal threads 3l and is adjustably positioned on the cylindrical extension 33 by virtue of its threaded engagement therewith, to provide longitudinal adjustment of the cone 34 relative to reduced diameter portion 39 to vary the cross-sectional area of the annular jet.

In Fig. 4 there is shownla further modification of a type of adjustable nozzle for use on a rocket motor employing a burster tube and having a. cylindrical extension for the nozzle. As illustrated, a housing 3 defining motor chamber 40 is provided having a reduced-diameter cylindrical extension 4I, which is internally threaded to receive a hollow externally threaded sleeve 42 having a forward outwardly flared portion 45.. A burster tube 43 is provided with a conical end 46 which projects into the extension 4I and is provided also with centralizing vanes 44 spaced about its periphery. Adjustment of the area of the annular throat formed between the conical end 45 of the burster tube 43 and the outwardly flared portion 45 of the cylindrical sleeve v42 may be obtained by rotating the sleeve 42 within the cylindrical portion 4 I.

In each of the foregoing embodiments of this invention manual adjustment of the throat area has been provided. However, in the embodiment of this invention illustrated in Figs. 5 and 6, there is shown a rocket motor in which the throat area is adjusted automatically with pressure. Referring now to Fig. 5, a housing 4 defining a motor chamber 5I is provided with a reduced-diameter cylindrical extension 52, the rear end of which is provided with radially projecting annular flange 50. A sleeve 53 having an outwardly flared forward portion 54 is slidably supported within the cylindrical extension 52 and is secured to an annular member or housing 55 by being threaded thereto.

An annular discharge passage is defined between flared portion 54 and the end of a burster tube 8B. Spaced fins 8| are suitably secured to the end of burster tube for centralizing purposes.

A helical compression spring 56 is inserted within the space defined by the annular member 55 and the outer surface of the cylindrical extension 52 of the rocket. A ring 51 is threaded into the forward end of the annular member 55 to retain spring 56 under compression and to provide means for adjusting the spring compression to adjust the force required to move the sleeve 53 rearwardly Within the cylindrical extension of the motor chamber. Spring 56 thus biases sleeve 53 forwardly to the position illustrated wherein the area of the annular discharge passage is a minimum. v

In operation, the gas pressure developed within motor chamber 5I operates on the forward facing fais/sacro surfaces of sleeve 3, and particularly on the flared portion 54 thereof to produce a rearward force on such sleeve proportional to the gas pressure. Such-rearward force is opposed by spring 56. By proper proportioning of spring 56 the resulting rearward movement of sleeve 53 and hence the area of the annular Idischarge passage may be controlled to maintain the pressureydveloped within motor chamber 5l substantially constant. f

In v, the modiiicationv illustrated in Fig. 6, a `cylindrical extension 1 l of a housing 5 defining'a motor chamber is provided with an inwardly 'projecting flange 'l2 at the rear thereof. "A hollow sleeve 13 is slidably inserted within extension H and has a forward outwardly flared portion 'll and a rear reduced diameter portion T4. A helical compression spring 15 is mounted within the annular recess defined between reduced diameter portion "i4 of sleeve 13 and extension TI and biases sleeve I3 forwardly. A flange 16 is suitably secured on the rear end of the adjustable sleeve 13 to retain the sleeve in the position illustrated wherein the area of the annular throat defined between flared end 11 of the sleeve 13 and a tapered portion T8 of a burster tube 80 is a mnimum. The movement of the sleeve within the cylindrical extension and against the coiled compression spring is automatic with pressure variations within the motor combustion chamber and provides automatically for an increase in the throat area of the annular jet in the manner previously described in connection with the structure of Fig. 5.

I claim:

1. In combination, a rocket motor chamber adapted to contain a material combustible to generate a hot propellant fluid under pressure, said chamber having a forwardly flared passage leading to a constricted orifice, a tube supported longitudinally within said chamber and adapted to contain a high explosive for fragmenting said chamber, one end of said tube being conical and including spaced fin members and extending into said constricted orice, a separately formed Venturi-like nozzle having a rearwardly flared exit passage extending from a constricted portion thereof, and means securing said nozzle to said chamber whereby said nozzle may be movable relative to said chamber to vary the cross-sectional area of the annular jet formed by the conical end of said tube and the constricted portion of said Venturi-like nozzle.

2. In combination, a rocket motor chamber adapted to contain a material combustible to generate a hot propellant iiuid under pressure, said chamber having a constricted exit orice for said uid, a conical member including spaced n members extending within said orifice in coaxial relation therewith and with its tip directed rearwardly to form an exhaust passage, and means for elfecting relative movement between said member and said orice for adjusting the cross-sectional area of said passage.

3. In combination, a rocket motor chamber adapted to contain a material combustible to generate a hot propellent gas under pressure, said chamber having a constricted exit orice for said gas, a conical member having spaced fin members supported within said chamber to extend within said orifice in coaxial relation therewith and with its apex directed rearwardly, a sleeve having a flared forward end and an open rear end, said sleeve being supported within said Amotor chamber and adjacent said,conical member toI form with said member an anr'nilar exhaust "passage for discharging said gas rearwardly, said fadapted to contain a propellent material and having a restricted exit orifice at rear end thereof, 'a' conical member having'space'd nmembers extending within said orifice to form an annular jeta sleevehaving a forwardly flared end positioned Within said orice and movable relative to said conical member for changing the cross-sectional area of said annular jet at its restricted portion, and means resiliently retaining said sleeve in a forward position within said oriflce to form with said conical member an annular jet of minimum cross-sectional area. whereby the fluid pressure within said chamber applied to the end section of said sleeve will move said sleeve rearwardly against said resilient means to increase the cross-sectional area of said annular jet.

5. In a rocket, a motor chamber adapted to contain a propellent material combustible to generate hot propellent gas under pressure, said chamber having a constricted exhaust passage comprising a cylinder extending rearwardly from said chamber, said cylinder being open at its rear end, sleeve means slidably fitting Within said cylinder and axially movable relatively thereto, said sleeve means having an outwardly ared forward end, and conical means including n means fixed in said chamber and coacting with the flared end of said sleeve to change the effective cross sectional area of said exhaust passage in response to sliding of said sleeve as a result of changes in pressure of propellent gas within said chamber.

6. In combination, a rocket motor chamber adapted to contain a propellent material combustible to generate a hot propellent fluid under pressure, said chamber having the wall thereof flared forwardly to form an entrance passage for said fluid leading to a constricted throat, a rearwardly flared exit passage for said fluid leading from said throat, a conical member having fins extending therefrom supported to extend within said throat to form an annular jet, and means for adjusting the relative axial position-s of said conical member and said throat.

'7. In a rocket, a casing forming a motor chamber, first means forming a constricted rearwardly-directed exhaust passage from said chamber and having an open rear end, conical means including fin means within the forward end of said exhaust passage, said n means maintaining said conical means in coaxial relation with said exhaust passage and means for effecting relative axial movement between .said first means and said conical means.

8. In a rocket, casing forming a motor chamber having a constricted rearwardly-directed exhaust passage, a cone having fins extending therefrom and having a rearwardly-directed apex and mounted within the forward end of said exhaust passage in coaxial relation therewith, and means for effecting relative axial adjustment of said cone and passage to thereby Vary the effective cross-sectional area of sai-d exhaust passage.

9. In a rocket, a casing forming a motor chamber terminating in a rearwardly-directed constricted extension having an open rear end, a.

sleeve slidably ttng within said extension and REFERENCES CITED v Aextend into the flared forward end of said sleeve having a ilared forward end within said cham- The followin references are of record the ber, a cone having spaced fins and mounted `to g le of this patent:

in coaxial relation therewith and with its apex 5 UNITED STATES PATENTS directed rearwardly, spring means between said Number Name Date extension and sleeve urging the latter into fOr- 1,838,354 Bauer Dec. 29, 1931 Ward position in which said cone and sleeve form 1,901,352 stolfa e1; a1, Mar. 14, 1933 a gas passage of minimum area, and stop means 2,402,809 Farr June 25, 1946 between said extension and sleeve, limiting the 1o forward movementl of said sleeve. FOREIGN PATENTS Number Country Date CLARENCE N. HICKMAN. 841,015 ,France Jan. 28, 1939 223,977 Switzerland J an. 18, 1943 

